High-speed integrated circuits often require the capacitors having a great capacitance density. For example, the bypass capacitors are often used for the reserving power and the decoupling capacitors are used to filter the fluctuating noises. Due to the small sizes of semiconductor chips, the capacitors embedded in the semiconductor dies can only have the large capacitances within the constrained area, often far smaller than required.
To increase the capacitance density of capacitors, discrete surface-mount capacitors were used, as illustrated in FIG. 1. The semiconductor chip 2 is electrically connected to the packaging substrate 4, which includes the plated vias 6. Through the routing metal traces 8, the semiconductor chip 2 is electrically connected to the vias 10, and further to the surface-mount capacitor 12. The surface-mount capacitor 12 is a discrete capacitor and hence can provide a very big capacitance.
The structure shown in FIG. 1 suffers from the drawbacks. In the high-frequency applications, the simultaneous switching noise (SSN) becomes an important factor for the system performance. The resonance modes of a parallel-plate waveguide as equivalent for the typical substrate structure can be excited by SSN and cause serious signal integrity and electromagnetic interference problems. Since the surface-mount capacitor 12 is usually spaced far away from the semiconductor chip 2, it has an inferior ability to suppress the SSN due to the large loop inductance.
To reduce the distance between capacitors and semiconductor chips, the embedded capacitors, which are formed inside the substrate, were developed. FIG. 2 schematically illustrates the conventional embedded capacitor 14, which includes the top electrode 16 and bottom electrode 18 separated by the insulating layer 20. One or both of the top electrode 16 and bottom electrode 18 may be formed in one of the existing layers of substrate 4, wherein the existing layers may include the signal layers, power layers, ground layers, and the like.
A typical method for increasing the capacitance of embedded capacitors shown in FIG. 2 is to fill in the insulating layer 20 with a very high dielectric constant material. However, it is very hard to find and process such materials. Even if such materials are available, the electrical performances of these materials are often not satisfactory. For example, DuPont provides a material having a dielectric constant of about 3000. However, the stop-bands of the resulting embedded capacitors do not have the central frequencies and bandwidths great enough for the high-frequency applications.
Accordingly, what is needed in the art is a semiconductor device that provides a high capacitance while at the same time overcoming the deficiencies of the prior art.